U.S. patent number 5,831,600 [Application Number 08/867,134] was granted by the patent office on 1998-11-03 for coordinate input device.
This patent grant is currently assigned to ALPS Electric Co, Ltd.. Invention is credited to Kinya Inoue, Hiroshi Shigetaka.
United States Patent |
5,831,600 |
Inoue , et al. |
November 3, 1998 |
Coordinate input device
Abstract
There is provided a coordinate input device in which when the
coordinate position of a contact portion on a tablet by a
coordinate input object is to be detected, influence of external
noise is minimized to improve the reliability of detection of the
coordinate position. The coordinate input device comprises a tablet
scanned by one scan signal selected from a plurality of scan
signals having different frequencies, and a coordinate data
generation section for generating coordinate data representing a
coordinate position of a contact portion when a coordinate input
object is brought into contact with the tablet, wherein when the
tablet is to be scanned with a scan signal, the coordinate data
formation section sequentially selects the plurality of scan
signals at least once a selecting operation, measures levels of
noise included in data output from the tablet each time the
selecting operation is performed, and then uses a scan signal
representing a minimum noise level of the measured noise levels to
scan the tablet.
Inventors: |
Inoue; Kinya (Fukushima-ken,
JP), Shigetaka; Hiroshi (Fukushima-ken,
JP) |
Assignee: |
ALPS Electric Co, Ltd.
(JP)
|
Family
ID: |
15300156 |
Appl.
No.: |
08/867,134 |
Filed: |
June 2, 1997 |
Foreign Application Priority Data
|
|
|
|
|
Jun 4, 1996 [JP] |
|
|
8-141787 |
|
Current U.S.
Class: |
345/173; 345/156;
345/174; 178/18.01; 178/18.02 |
Current CPC
Class: |
G06F
3/044 (20130101); G06F 3/04182 (20190501); G06F
3/0446 (20190501) |
Current International
Class: |
G06F
3/033 (20060101); G09G 005/00 () |
Field of
Search: |
;345/173,174,179,156,177,471XY ;178/18,19 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hofsass; Jeffery A.
Assistant Examiner: Lieu; Julie
Attorney, Agent or Firm: Brinks Hofer Gilson & Lione
Claims
What is claimed is:
1. A coordinate input device comprising an operation area scanned
by one scan signal selected from a plurality of scan signals having
different frequencies, and coordinate data formation means for
generating coordinate data representing a coordinate position of a
contact portion when a coordinate input object is brought into
contact with said operation area, characterized in that said
coordinate data formation means sequentially selects the plurality
of scan signals at least once a selecting operation to scan said
operation area, measures levels of noise included in data output
from said operation area each time the selecting operation is
performed, and then uses a scan signal representing a minimum noise
level of the measured noise levels to scan said operation area.
2. A coordinate input device according to claim 1, characterized in
that the measured noise levels are stored in a memory in
correspondence with the frequencies of the sequentially selected
scan signals.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coordinate input device and,
more particularly, to a coordinate input device in which when a
coordinate input object is brought into contact with an operation
area to operate the operation area, influence of external noise on
coordinate data representing the coordinate position of a
coordinate input object contact portion is minimized.
2. Description of the Related Art
In recent years, a coordinate input device used by the following
manner has developed. That is, when a coordinate input object such
as an input pen or a finger is brought into contact with a desired
position of a tablet-type operation area, coordinate data
representing the coordinate positions of the contact portions are
sequentially output to display the contact positions of the
coordinate input object.
Here, FIG. 4 is a block diagram showing a known coordinate input
device.
As shown in FIG. 4, the coordinate input device is constituted by a
tablet 51, a coordinate input object 52 such as an input pen or a
finger of an operator, a coordinate data generator 53, and a signal
processor 54 such as a personal computer (PC).
The tablet 51 is arranged to be perpendicular to the front and rear
surfaces of a substrate (not shown), and is constituted by a
plurality of (N) electrodes 55 (X.sub.1 to X.sub.N) and a plurality
of (M) electrodes 56 (Y.sub.1 to Y.sub.M) which are arranged in a
matrix, a protective film (not shown) adhered to the upper surface
of the substrate, and the like. The input pen 52 has a tip and a
surface which consist of a conductive material. The coordinate data
generator 53 is constituted by an X-axis side multiplexer 57, a
Y-axis side multiplexer 58, a first amplification circuit 59, a
first filter circuit 60, an analog/digital converter (A/D) 61, a
controller (CPU) 62, an oscillation circuit 63, and an analog
switch 64. In this case, the X-axis side multiplexer 57 has a
plurality of (N) switches S.sub.1 to S.sub.N which are arranged in
parallel in each other. One ends of the switches S.sub.1 to S.sub.N
are connected to one ends of the X electrodes 55 (X.sub.1 to
X.sub.N), respectively, and the other ends of the switches S.sub.1
to S.sub.N are connected to the analog switch 64 in common. The
Y-axis side multiplexer 58 has a plurality of (M) switches S.sub.1
to S.sub.M which are arranged in parallel. One ends of the switches
S.sub.1 to S.sub.M are connected to one ends of the Y electrodes 56
(Y.sub.1 to Y.sub.M), respectively, and the other ends of the
switches S.sub.1 to S.sub.M are connected to the input terminal of
the first amplification circuit 59 in common. One input terminal of
the first filter circuit 60 is connected to the output terminal of
the first amplification circuit 59, and the output terminal of the
first filter circuit 60 is connected to the input terminal of the
A/D converter 61. The CPU 62 has a data output terminal connected
to the signal processor 54, and has a control terminal connected to
the control terminal of the analog switch 64.
An operation of a known coordinate input device having the above
arrangement will be briefly described below.
A case wherein the tablet 51 is operated with a finger 52 of an
operator will be described. An oscillation signal from the
oscillation circuit 63 is supplied to the X-axis side multiplexer
57. At this time, the switches S.sub.1 to S.sub.N of the X-axis
side multiplexer 57 and the switches S.sub.1 to S.sub.M of the
Y-axis side multiplexer 58 are ON/OFF-controlled with a control
signal supplied from the CPU 62. The manner of this control is as
follows. That is, the switch S.sub.1 of the X-axis side multiplexer
57 is turned on first, and the switches S.sub.1 to S.sub.M of the
Y-axis side multiplexer 58 are sequentially turned on. The switch
S.sub.2 of the X-axis side multiplexer 57 is turned on, the
switches S.sub.1 to S.sub.M of the Y-axis side multiplexer 58 are
sequentially turned on. Similarly, with respect to the switches
S.sub.3 to S.sub.M of the X-axis side multiplexer 57, one of these
switches is turned on, and the switches S.sub.1 to S.sub.M of the
Y-axis side multiplexer 58 are sequentially turned on. With the
above scanning operation, oscillation signals from the oscillation
circuit 63 are sequentially supplied to the X electrodes 55
(X.sub.1 to X.sub.N), and the signal voltages of the oscillation
signals generate electrostatic capacitors between the X electrodes
55 (X.sub.1 to X.sub.N) and the Y electrodes 56 (Y.sub.1 to
Y.sub.M).
Here, when the finger 52 is brought into contact with a desired
position on the tablet 51, some of electric lines of force
generated by a capacitor near the contact position are absorbed by
the finger 52, the capacitance of the electrostatic capacitor
located at this portion, and the signal voltage extracted from the
portion decreases according to a decrease in the capacitance. With
the scanning operation of the X-axis side multiplexer 57 and the
Y-axis side multiplexer 58, the signal voltages output from the Y
electrodes 56 (Y.sub.1 to Y.sub.M) are amplified by the first
amplification circuit 59, and the signal voltages from which noise
components are removed by the first filter circuit 60 are supplied
to the A/D 61. The A/D 61 converts the input signal voltages into
digital signals, and the CPU 62 loads the digital signals. The CPU
62 calculates the Y and X electrodes 56 and 55 each having the
smallest signal voltage value on the basis of the loaded digital
signals to detect a contact position of the finger 52 on the tablet
51.
In this manner, when detection for the X- and Y-coordinates of the
position where the finger 52 touches on the tablet 51 is made, the
CPU 62 sends the detection data to the signal processor 54. In the
signal processor 54, a cursor corresponding to the contact position
of the finger 52 and displayed on the display unit is moved.
When the tablet 51 is operated with the input pen 52, a generated
electrostatic capacitance is absorbed by a hand holding the finger
52 through the input pen 52 to detect the X and Y coordinates of
the finger 52 as described above.
In this known coordinate input apparatus, when the coordinate
position of the contact portion on the tablet (scanning area) 51 is
detected by a coordinate input object such as the input pen 52, the
switches S.sub.1 to S.sub.N of the X-axis side multiplexer 57 are
sequentially turned on to scan the X electrodes 55 (X.sub.1 to
X.sub.N), and the switches S.sub.1 to S.sub.M of the Y-axis side
multiplexer 58 are sequentially turned on to scan the Y electrodes
56 (Y.sub.1 to Y.sub.M). Scan signals used when these scanning
operations have specific frequencies, respectively.
In the known coordinate input device, when signal voltages are read
from the tablet 51, external noise is superposed on the read signal
voltages. In this case, most of the external noise superposed on
the signal voltages is removed by the first filter circuit 60 or a
second filter circuit 66. However, when the external noise
frequency is approximate to the frequency of the scan signal, the
external noise cannot be removed by the first filter circuit 60 or
the second filter circuit 66, and the signal voltages are input to
the A/D 61 and the CPU 62 without removing the external noise from
the signal voltages. For this reason, the external noise adversely
affects detection of a coordinate position by the CPU 62, and the
reliability of detection of the coordinate position is
degraded.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problem, and has
as its object to provide a coordinate input device in which when a
coordinate position of a contact portion on an operation area by a
coordinate input object is to be detected, influence of external
noise is minimized to improve the reliability of detection of the
coordinate position.
In order to achieve the above object, a coordinate input device
according to the present invention comprises means for preparing a
plurality of scan signals having frequencies different from those
of scan signals for scanning an operation area, sequentially
scanning the operation area by the plurality of scan signals,
measuring external noise superposed on data output from the
operation area each time the scan signals are changed, and then
selecting a scan signal on which external noise at the minimum
level is superposed to scan the operation area.
According to this means, when data is output from the scanned
operation area, the scan signal on which the external noise at the
minimum level is superposed can be selected. For this reason,
influence of the external noise can be minimized, and the
reliability of detection of the coordinate position can be
improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a coordinate input device
according to an embodiment of the present invention.
FIG. 2 is a development showing an arrangement of a tablet used in
the coordinate input device shown in FIG. 1.
FIG. 3 is a flow chart showing the details of an operation
performed when the frequencies of scan signals are sequentially
updated in the coordinate input device shown in FIG. 1.
FIG. 4 is a block diagram showing a conventional coordinate input
device.
DESCRIPTION OF THE PREFERRED EMBODIMENT
According to an embodiment of the present invention, a coordinate
input device comprises an operation area scanned by one scan signal
selected from a plurality of scan signals having different
frequencies, and coordinate data formation means for generating
coordinate data representing a coordinate position of a contact
portion when a coordinate input object is brought into contact with
the operation area, wherein the coordinate data formation means
sequentially selects the plurality of scan signals at least once a
selecting operation to scan the operation area, measures levels of
noise included in data output from the operation area each time the
selecting operation is performed, and then uses a scan signal
representing a minimum noise level of the measured noise levels to
scan the operation area.
At this time, the measured noise levels are stored in a memory in
correspondence with the frequencies of the sequentially selected
scan signals.
According to this embodiment, the operation area to be scanned by a
scan signal is scanned such that a plurality of scan signals having
different frequencies are sequentially selected at least once a
selecting operation, and, at this time, levels of external noise
superposed on data output from the operation area are measured.
Thereafter, the operation area is scanned by a scan signal having
external noise at the minimum level. For this reason, when the
coordinate input object is brought into contact with the operation
area, and the coordinate position of the contact portion is to be
detected, influence of the external noise superposed on the
coordinate data can be minimized. As a result, the reliability of
detection of the coordinate position can be improved.
EMBODIMENT
An embodiment of the present invention will be described below with
reference to the accompanying drawings.
FIG. 1 is a block diagram showing a coordinate input device
according to an embodiment of the present invention. FIG. 2 is a
development showing an arrangement of a tablet used in the
coordinate input device shown in FIG. 1.
As shown in FIG. 1, the coordinate input device is constituted by a
tablet (operation area) 1, a coordinate input object 2 such as an
input pen 2-1 or a finger 2-2 of an operator, a coordinate data
generation section 3, and a signal processor 4 such as a personal
computer (PC).
The tablet 1, as shown in FIG. 2, is constituted by a film
substrate 5, a plurality of (N) parallel X electrodes 6 (X.sub.1 to
X.sub.N) formed on the upper surface of the film substrate 5, a
plurality of (M) parallel Y electrodes 7 (Y.sub.1 to Y.sub.M) which
are adhered to the lower surface of the film substrate 5 and
arranged perpendicularly to the X electrodes 6 (X.sub.1 to
X.sub.N), a protective film 8 adhered to the upper surface of the
film substrate 5, and a shield film 9 adhered to the lower surface
of the film substrate 5. The tablet 1 is incorporated in the
keyboard of the personal computer to function as a mouse.
The coordinate data generation section 3, as shown in FIG. 1, is
constituted by an X-axis side multiplexer 17 having a plurality of
(N) switches S.sub.1 to S.sub.N arranged in parallel, a Y-axis side
multiplexer 18 having a plurality of (M) switches S.sub.1 to
S.sub.M arranged in parallel, a first amplification circuit 19, a
first filter circuit 20, an analog/digital converter (A/D) 21, a
controller (CPU) 22, an oscillation circuit 23, a first drive
selection circuit 24 constituted by a switch, a second drive
selection circuit 30, a second amplification circuit 25, a second
filter circuit 26, noise level measurement section 27, a scan
signal switching section 28, and a memory 29. In this case, the
noise level measurement section 27 measures the noise amount and
noise level (the maximum value of the noise amount--the minimum
value of the noise amount) of external noise superposed on a
digital signal supplied to the filter constant setting section 22,
and the scan signal switching section 28 switches a scan signal
output from the CPU 22 to signals having a plurality of
frequencies, e.g., any one of first to eighth scan signals having
frequencies f1 to f8. The memory 29 stores the noise levels
measured by the noise level measurement section 27 in
correspondence with the frequencies f1 to f8 when the scan signal
is switched to the first to eighth scan signals. In the coordinate
data generation section 3, the first and second drive selection
circuits 24 and 30 are added, and the noise level measurement
section 27, the scan signal switching section 28, and the memory 29
are connected to the CPU 22.
An operation of the coordinate input device according to this
embodiment with the above arrangement will be described below.
In the coordinate input device according to this embodiment, the
frequency of a scan signal for turning on all the switches S.sub.1
to S.sub.N of the X-axis side multiplexer 17 on to scan the X
electrodes 6 (X.sub.1 to X.sub.N) of the tablet 1 is set, and the
switches S.sub.1 to S.sub.M of the Y-axis side multiplexer 18 are
sequentially turned on. The frequency of a scan signal for turning
on all the switches S.sub.1 to S.sub.M of the Y-axis side
multiplexer 18 to scan the Y electrodes 7 (Y.sub.1 to Y.sub.M) of
the tablet 1 is set to be equal to the frequency of the scan signal
for the X axis, and the switches S.sub.1 to S.sub.N of the X-axis
side multiplexer 17 are sequentially turned on.
More specifically, the oscillation circuit 23 outputs a scan signal
having a frequency determined by a control signal from the CPU 22,
and outputs the scan signal to the X-axis side multiplexer 17
first. In this case, the amplification circuit 25 is in an OFF
state by a switching operation of the first drive selection circuit
24.
On the other hand, connection from the oscillation circuit 23 is
turned off by the second drive selection circuit 30, and the first
amplification circuit 19 is connected to the Y-axis side
multiplexer 18.
In the X-axis side multiplexer 17, the switches S.sub.1 to S.sub.N
are sequentially turned on by a control signal from the CPU 22, and
a voltage is extracted to the amplification circuit 19.
The first drive selection circuit 24 is turned off by a control
signal from the CPU 22 together with the oscillation circuit 23,
and the X-axis side multiplexer 17 and the amplification circuit 25
are connected to each other. The second drive selection circuit 30
is connected to the oscillation circuit 23 and outputs a scan
signal from the oscillation circuit 23 to the Y-axis side
multiplexer 18. The Y-axis side multiplexer 18 and the
amplification circuit 19 are turned off.
Here, an operation performed in a case wherein the frequencies of
scan signals for scanning the X electrodes 6 (X.sub.1 to X.sub.N)
and/or the frequencies of scan signals for scanning the Y
electrodes 7 (Y.sub.1 to Y.sub.M) are sequentially changed will be
described below with reference to the flow chart shown in FIG. 3,
i.e., the flow chart showing the details of an operation performed
when the frequencies of scan signals are sequentially changed in
the coordinate input device according to this embodiment.
In step S1, the CPU 22 generates, of the first to eighth scan
signals which can be generated, one scan signal having a minimum
noise level in previous noise level measurement, e.g., the first
scan signal, and sequentially turns on the switches S.sub.1 to
S.sub.N of the X-axis side multiplexer 17 to scan the X electrodes
6 (X.sub.1 to X.sub.N) of the tablet 1.
In step S2, signal voltages obtained at the Y electrodes 7 (Y.sub.1
to Y.sub.M) of the tablet 1 are sequentially extracted through the
Y-axis side multiplexer 18 whether the tablet 1 is operated by the
input pen 2-1 or not. The signal voltages are amplified by the
first amplification circuit 19, and the noise component of the
signal voltages are removed by the first filter circuit 20. The
signal voltages are converted into digital signals by the A/D 21.
The resultant digital signals are loaded on the CPU 22.
In step S3, the CPU 22 measures the X coordinate of the tablet 1 on
the basis of the loaded digital signals.
In step S4, the CPU 22 measures the Y coordinate of the table 1 on
the basis of the loaded digital signals.
In step S5, on the basis of the loaded digital signals, the CPU 22
measures a Z coordinate representing that the input pen 2-1 is
close to or brought into contact with the tablet 1.
In step S6, the CPU 22 supplies the loaded digital signals to the
noise level measurement section 27 to measure an amount of external
noise superposed on the digital signals.
Subsequently, in step S7, the CPU 22 checks whether the Z
coordinate measured in step S5 exceeds a threshold value, i.e.,
whether the input pen 2-1 is close to or brought into contact with
the tablet 1. If it is determined that the Z coordinate does not
exceed the threshold value (N), the flow shifts to next step S8. If
it is determined that the Z coordinate exceeds the threshold value
(Y), the flow shifts to other step S9.
In step S8, the CPU 22 drives the scan signal switching section 28
to generate one scan signal having a minimum noise level in the
previous noise level measurement, e.g., the second scan signal, as
a scan signal for sequentially turning on the switches S.sub.1 to
S.sub.N of the X-axis side multiplexer 17. Thereafter, the CPU 22
sequentially turns on the switches S.sub.1 to S.sub.N of the X-axis
side multiplexer 17 to scan the X electrodes 6 (X.sub.1 to X.sub.N)
of the tablet 1.
In step S9, the CPU 22 supplies the loaded digital signals to the
noise level measurement section 27 and measures a noise level in
the scan signal, i.e., a noise level obtained by subtracting the
minimum noise level from the maximum noise level.
In step S10, the CPU 22 checks whether the number of measurements
of noise levels in step S9, i.e., a measurement count is equal to
the total number (8) of the first to eighth scan signals. If it is
determined that the measurement count is equal to 8 (Y), the flow
shifts to step S11. If it is determined that the measurement count
is not equal to 8 (N), the flow returns to the first step (step S1)
to execute the processes in steps following step S1 again.
In step S11, on the basis of the digital signals supplied to the
noise level measurement section 27, the CPU 22 temporarily stores
noise levels in a scanning operation (sequential change cycles of
previous scan signals) by the previous first to eighth scan signals
measured by the noise level measurement section 27 in a temporary
storage section of the memory 29 in correspondence with the
frequencies f1 to f8 of the first to eighth scan signals.
In step S12, the CPU 22 converts the noise levels in the sequential
change cycles of the previous scan signals temporarily stored in
the temporary storage section of the memory 29 are converted into
noise levels in sequential change cycles of current scan
signals.
Subsequently, in step S13, the CPU 22 causes sequential change
cycles of scan signals for sequentially changing the scan signals
of the X-axis side multiplexer 17 to shift from sequential change
cycles of the current scan signals to sequential change cycles of
the next scan signals.
In step S14, the CPU 22 sets the number of measurements of noise
levels, i.e., a measurement count, to be 0 at step S9. Upon
completion of this setting, the flow returns to step S1 to execute
the processes in steps following step S1 again.
In step S15, the CPU 22 selects one scan signal having the minimum
noise level in the previous stage, e.g., the second scan signal,
and sequentially turns on the switches S.sub.1 to S.sub.N of the
X-axis side multiplexer 17 by the second scan signal. In this
state, when the CPU 22 scans the X electrodes 6 (X.sub.1 to
X.sub.N) of the tablet 1, the CPU 22 checks whether the Z
coordinate exceeds the threshold value once (or 0 times). If it is
determined that the Z coordinate exceeds the threshold value once
(Y), the flow shifts to next step S16. If it is determined that the
Z coordinate exceeds the threshold value 0 times (N), the flow
returns to the first step, i.e., step S1, to execute the processes
in steps following step S1 again.
In step S16, the CPU 22 supplies the digital signals to the noise
level measurement section 27 to measure a current noise level. If
the measurement index of the noise level at this time is worst,
i.e., 255 (0 is the best, the measurement index becomes worse with
an increase in integer value, and 255 is worst) or is approximate
to 255, the flow immediately shifts to next step S17.
In step S17, the CPU 22 drives the scan signal switching section 28
to generate another scan signal, e.g., the third scan signal, in
place of one scan signal selectively generated in step S8, e.g.,
the second scan signal, as a scan signal for sequentially turning
on the switches S.sub.1 to S.sub.N of the X-axis side multiplexer
17. When the third scan signal is generated, the flow returns to
step S1 to execute the processes in steps following step S1
again.
In this manner, according to this embodiment, when the tablet
(operation area) 1 is to be scanned by a scan signal, a plurality
of scan signals having different frequencies are sequentially
selected at least once a selecting operation as scan signals,
levels of external noise superposed on data output from the tablet
1 in a scanning operation by the selected scan signal are measured.
Thereafter, the tablet 1 is scanned by a scan signal having
external noise at the minimum level. For this reason, when the
coordinate input object 2 is brought into contact with the tablet
1, and the coordinate position of the contact portion is to be
detected, influence of the external noise superposed on the
coordinate data can be minimized. As a result, the reliability of
detection of the coordinate position can be improved.
The above embodiment has been described by using a case wherein 8
scan signals, i.e., the first to eighth scan signals are used.
However, the total number of scan signals is not limited to 8, and
a number other than 8 may be selected as the total number of scan
signals as a matter of course.
As has been described above, according to the present invention,
when an operation area is to be scanned by a scan signal, a
plurality of scan signals having different frequencies are
sequentially selected at least once a selecting operation as scan
signals, the operation area is scanned by the selected scan signal
to obtain data, and the level of external noise superposed on the
obtained data is measured. Thereafter, the operation area is
scanned by a scan signal having external noise at the minimum
level. For this reason, when the coordinate input object is brought
into contact with the operation area, and the coordinate position
of the contact portion is to be detected, influence of the external
noise superposed on the coordinate data can be minimized. As a
result, the reliability of detection of the coordinate position can
be advantageously improved.
* * * * *